The NEP inhibitor prodrug sacubitril (N-(3-carboxyl-1-oxopropyl)-(4S)-(p-phenylphenylmethyl)-4-amino-(2R)-methyl butanoic acid ethyl ester; IUPAC name 4-{[(1S,3R)-1-([1,1′-biphenyl]-4-ylmethyl)-4-ethoxy-3-methyl-4-oxobutyl]amino}-4-oxobutanoic acid) is represented by the following formula (A)

Sacubitril together with valsartan, a known angiotensin receptor blocker (ARB), forms a sodium salt hydrate complex, known as LCZ696, comprising the anionic forms of sacubitril and valsartan, sodium cations and water molecules in the molar ratio of 1:1:3:2.5, respectively (ratio of 6:6:18:15 in the asymmetric unit cell of the solid state crystal), and which is schematically present in formula (B).

Said complex is also referred to by the following chemical names: Trisodium [3-((1S,3R)-1-biphenyl-4-ylmethyl-3-ethoxycarbonyl-1-butylcarbamoyl)propionate-(S)-3′-methyl-2′-(pentanoyl{2″-(tetrazol-5-ylate)biphenyl-4′-ylmethyl}amino)butyrate] hemipentahydrate or Octadecasodium hexakis(4-{[(1S,3R)-1-([1,1′-biphenyl]-4-ylmethyl)-4-ethoxy-3-methyl-4-oxobutyl]amino}-4-oxobutanoate) hexakis(N-pentanoyl-N-{[2′-(1H-tetrazol-1-id-5-yl)[1,1′-biphenyl]-4-yl]methyl}-L-valinate)-water (1/15) (IUPAC nomenclature).
LCZ696 acts as angiotensin receptor neprilysin inhibitor (ARNI) and is therefore useful particularly in the treatment of hypertention or chronic heart failure. Its utility has been confirmed by clinical trials, e.g. in the landmark PARADIGM-HF trial.
Chemical synthesis routes to prepare NEP inhibitors and their prodrugs, in particular sacubitril, and its precursors have been described previously, e.g. in Ksander et al. J. Med. Chem. 1995, 38, pp. 1689-1700; in U.S. Pat. No. 5,217,996 and in the international patent applications WO 2008/031567, WO 2008/083967, WO 2009/090251, WO 2010/081410, WO 2011/035569, WO 2011/088797, WO 2012/025501, WO 2012/025502 and WO 2014/032627.
However, there is still a need to design a chemical process for the synthesis of sacubitril which is suitable for industrial scale production under economically and environmentally favorable conditions and provides the drug substance in high chemical purity and with high stereo-chemical selectivity.